This invention pertains to stepping motors and, more particularly, to the damping of the oscillations that occur when a stepping motor is stopped at a desired position.
There are many times when it is required to rapidly and precisely position a rotatable member. Two of the more common applications are in the rotation of a lead screw to rectilinearly position a member and also in the rotation of a print element such as a "daisy wheel" to select characters. Heretofore, the precise positioning of such members was accomplished by the utilization of complex and expensive servo systems incorporating DC motors. However, there is disclosed in U.S. Pat. No. 4,215,302 methods and apparatus for driving a rotatable member by merely using a stepping motor which is energized by particular current waveforms. Thus, the complexity and expense is minimized since inexpensive stepping motors without complex servo systems can be employed. While the methods and apparatus shown in said patent are eminently satisfactory for many uses, it has been found that at the time of stopping there is a small oscillation of the rotor. In U.S. Pat. No. 3,947,742 there is another approach to solving the same problem of a motor driving a load. This approach in addition to many practical problems, does not take into account the second order effects which cause, at the time of stopping, the same small oscillations. While, for many uses, these oscillations are insignificant, there are occasions when the application demands a very rapid damping of such oscillations.